Cooling device for internal combustion engine

ABSTRACT

An ECU performs a failure diagnosis for a thermostat valve after starting of an engine based on an output of an engine-side coolant water temperature sensor and an output of a radiator-side coolant water temperature sensor. When an electric pump operates in accordance with a heating request or the like of an air-conditioning device during stopping of the engine, the thermostat valve attains a closed state. When the electric pump operates during stopping of the engine before the current starting of the engine, starting of the failure diagnosis performed after starting of the engine is delayed as compared to the case where the electric pump does not operate during stopping of the engine. Consequently, erroneous determination can be suppressed in the failure diagnosis for the thermostat valve.

This nonprovisional application is based on Japanese Patent ApplicationNo. 2013-250213 filed on Dec. 3, 2013 with the Japan Patent Office, theentire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a cooling device for an internalcombustion engine, and particularly to a technique of diagnosing afailure of a thermostat valve provided in a cooling device for aninternal combustion engine.

2. Description of the Background Art

Japanese Patent Laying-Open No. 2010-196587 discloses an abnormalitydetecting device for detecting an abnormality of a thermostat valveprovided in an engine cooling system of a hybrid vehicle capable ofperforming EV traveling of stopping an engine and traveling with a driveforce of a motor. An increase in the EV traveling reduces an opportunityto operate an engine and in turn reduces an opportunity to detect anabnormality of a thermostat valve. According to this abnormalitydetecting device, engine coolant water is heated by a heater during theEV traveling, and if a temperature of the engine coolant water rises tobe higher than or equal to a determination temperature, it is determinedthat a thermostat valve operates normally (Japanese Patent Laying OpenNo. 2010-196587).

Heat of coolant water heated by exhausted heat of an engine can beutilized for heating or the like performed by an air-conditioningdevice, and even during stopping of the engine, circulation of coolantwater by operation of an electric pump in accordance with a heatingrequest or the like of the air-conditioning device may occur. In thiscase, since the engine is stopped, the thermostat valve is closed, andthe coolant water circulates without passing through a radiator.Accordingly, a situation may occur which causes the temperature of thecirculating coolant water to be lower than a temperature of coolantwater remaining in a radiator circulation passage for allowing coolantwater to flow into the radiator.

When the engine is started in such a situation, and a failure diagnosisfor the thermostat valve is executed, erroneous determination ispossibly made in the failure diagnosis due to the reversed relationshipbetween the temperature of the circulating coolant water and thetemperature of the coolant water remaining in the radiator circulationpassage.

SUMMARY OF THE INVENTION

The present invention was made to solve the problem described above, andits object is to suppress erroneous determination in a failure diagnosisfor a thermostat valve provided in a cooling device for an internalcombustion engine.

A cooling device for an internal combustion engine according to thepresent invention includes a coolant water passage formed in theinternal combustion engine, a radiator cooling coolant water, a radiatorcirculation passage, a bypass passage, a heat exchanger, a thermostatvalve, an electric pump, first and second temperature sensors, and acontrol device. The radiator circulation passage is configured to allowcoolant water discharged from the coolant water passage to pass throughthe radiator and return to the coolant water passage. The bypass passageis configured to allow coolant water discharged from the coolant waterpassage to return to the coolant water passage without passing throughthe radiator. The heat exchanger is provided on the bypass passage andutilizes heat of the coolant water. The thermostat valve is connected tothe radiator circulation passage and the bypass passage, and switched,in accordance with a temperature of coolant water flowing in thethermostat valve, to either a closed state of intercepting coolant waterfrom the radiator circulation passage and outputting coolant water fromthe bypass passage to the coolant water passage, or an opened state ofoutputting coolant water from the radiator circulation passage andcoolant water from the bypass passage to the coolant water passage. Theelectric pump allows coolant water to circulate. The first temperaturesensor detects a temperature of coolant water in the coolant waterpassage. The second temperature sensor detects a temperature of coolantwater in the radiator circulation passage. The control device performs afailure diagnosis for the thermostat valve after starting of theinternal combustion engine based on an output of the first temperaturesensor and an output of the second temperature sensor. When the electricpump operates in accordance with an operation request of the heatexchanger during stopping of the internal combustion engine, thethermostat valve attains the closed state. In a case where the electricpump operates during stopping of the internal combustion engine, thecontrol device delays starting of the failure diagnosis performed afterstarting of the internal combustion engine as compared to a case wherethe electric pump does not operate during stopping of the internalcombustion engine.

In this cooling device for an internal combustion engine, in the casewhere the electric pump operates in accordance with the operationrequest of the heat exchanger during stopping of the internal combustionengine, starting of the failure diagnosis performed after starting ofthe internal combustion engine is delayed as compared to the case wherethe electric pump does not operate during stopping of the internalcombustion engine. Therefore, starting of the failure diagnosis for thethermostat valve is avoided in a state where the relationship betweenthe temperature of the coolant water in the coolant water passage andthe temperature of the coolant water in the radiator circulation passageare inversed. Thus, according to the cooling device for an internalcombustion engine, erroneous determination in the failure diagnosis forthe thermostat valve can be suppressed.

Preferably, the control device starts the failure diagnosis when a risequantity (ΔECT) of a coolant water temperature, which is detected by thefirst temperature sensor, from starting of the internal combustionengine exceeds a predetermined value. A first value indicating thepredetermined value for the case where the electric pump operates duringstopping of the internal combustion engine is larger than a second valueindicating the predetermined value for the case where the electric pumpdoes not operate during stopping of the internal combustion engine.

The failure diagnosis of the thermostat valve is performed based on thecoolant water temperature. According to the cooling device for aninternal combustion engine, starting of the failure diagnosis isadjusted based on the coolant water temperature. Therefore, a starttiming of the failure diagnosis can be adjusted with a high accuracy.

Moreover, preferably, the control device integrates an intake air volumeto the internal combustion engine from starting of the internalcombustion engine, and starts the failure diagnosis when the integratedvalue of the intake air volume exceeds a predetermined value. A firstvalue indicating the predetermined value for the case where the electricpump operates during stopping of the internal combustion engine islarger than a second value indicating the predetermined value for thecase where the electric pump does not operate during stopping of theinternal combustion engine.

The integrated amount of the intake air volume to the internalcombustion engine may represent a tendency of a rise in the temperatureof the internal combustion engine and of the coolant water. Therefore,in this cooling device for an internal combustion engine, starting ofthe failure diagnosis is adjusted based on the integrated amount of theintake air volume. Thus, this cooling device for an internal combustionengine can also suppress erroneous determination in the failurediagnosis for the thermostat valve.

Moreover, preferably, the control device starts the failure diagnosiswhen an elapsed time from starting of the internal combustion engineexceeds a predetermined value. A first value indicating thepredetermined value for the case where the electric pump operates duringstopping of the internal combustion engine is larger than a second valueindicating the predetermined value for the case where the electric pumpdoes not operate during stopping of the internal combustion engine.

In this cooling device for an internal combustion engine, starting ofthe failure diagnosis is adjusted based on the elapsed time fromstarting of the internal combustion engine. Therefore, a process forcapturing a detection signal of a sensor and a calculation process arenot required. Thus, according to this cooling device for an internalcombustion engine, the process of the control device can be simplified.Moreover, starting of the failure diagnosis can be adjusted withoutbeing affected by an abnormality of a sensor and a measurement accuracy

Preferably, the control device calculates an estimation value of thecoolant water temperature in the radiator circulation passage based on aleakage flow rate through the radiator circulation passage in the closedstate of the thermostat valve and on an output of the first temperaturesensor, and diagnoses that the thermostat valve is failed in a casewhere an output value of the second temperature sensor is larger thanthe calculated estimation value.

According to this cooling device for an internal combustion engine, thefailure diagnosis of the thermostat valve is performed taking intoconsideration the leakage flow rate through the radiator circulationpassage in the closed state of the thermostat valve. Therefore, thefailure diagnosis can be performed with a high accuracy.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents a schematic configuration of a vehicle including acooling device for an internal combustion engine according to anembodiment of the present invention.

FIG. 2 represents one example of a change in an engine coolant watertemperature before and after starting the engine.

FIG. 3 is a flowchart for describing procedures of the thermostat valvefailure diagnosis process executed by the ECU shown in FIG. 1.

FIG. 4 is a flowchart representing process procedures for determiningthe diagnosis precondition shown in FIG. 3.

FIG. 5 is a flowchart representing process procedures for determining adiagnosis precondition in Modified Example 1.

FIG. 6 is a flowchart representing process procedures for determining adiagnosis precondition in Modified Example 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, the embodiment of the present invention will bedescribed in detail with reference to the drawings. It should be notedthat the same or corresponding parts in the drawings have the samereference numerals allotted and description thereof will not berepeated.

FIG. 1 represents a schematic configuration of a vehicle including acooling device for an internal combustion engine according to theembodiment of the present invention. Referring to FIG. 1, a vehicle 100includes an engine 20, an engine cooling device 10 for cooling engine20, and a thermal component 300.

Engine cooling device 10 includes an electric water pump (hereinafter,referred to as “electric pump”) 30, a radiator 40, a radiatorcirculation passage 50, a bypass passage 60, and a thermostat valve 70.Moreover, engine cooling device 10 further includes an engine-sidecoolant water temperature sensor 80, a radiator-side coolant watertemperature sensor 90, and a control device (hereinafter, also referredto as “ECU (Electronic Control Unit)”) 200.

Engine 20 has a water jacket 24 for cooling engine 20 by means ofcoolant water. Water jacket 24 is formed around cylinders of engine 20and constitutes a coolant water passage 25 allowing coolant water topass therethrough. Coolant water passage 25 is provided between an inlet27 and an outlet 26, and allows coolant water from inlet 27 to be sentout from outlet 26. The coolant water flowing into coolant water passage25 performs a heat exchange with engine 20 to cool engine 20.Accordingly, engine 20 is maintained at a temperature which is suitablefor combustion.

Electric pump 30 is a pump driven by an electric motor to circulatecoolant water of engine 20. Electric pump 30 is mounted to anattachment-side surface portion 22 of an engine main body. Electric pump30 allows coolant water to be sent out from inlet 27 into coolant waterpassage 25.

Driving and stopping of electric pump 30 is controlled by a controlsignal received from ECU 200. Further, a discharge amount of coolantwater discharged from electric pump 30 is controlled by a control signalreceived from ECU 200.

Outlet 26 constitutes a branch portion 120. Branch portion 120 isconnected to radiator circulation passage 50 and bypass passage 60.Branch portion 120 separates coolant water from coolant water passage 25into coolant water directed to radiator circulation passage 50 andcoolant water directed to bypass passage 60.

Radiator circulation passage 50 is a passage for circulating coolantwater between engine 20, electric pump 30, and radiator 40. Radiatorcirculation passage 50 is constituted by pipes 50 a, 50 b and radiator40. Pipe 50 a is provided between branch portion 120 and an inlet 42 ofradiator 40. Pipe 50 b is provided between an outlet 44 of radiator 40and thermostat valve 70. Coolant water warmed up in engine 20 passesthrough radiator 40 and is cooled.

Radiator 40 performs a heat exchange between coolant water flowing inradiator 40 and outside air to thereby radiate heat of the coolantwater. Radiator 40 is provided with cooling fans 46. Cooling fan 46accelerates a heat exchange through ventilation to improve aheat-radiation efficiency of the coolant water in radiator 40. Coolantwater cooled in radiator 40 is sent out from outlet 44.

Bypass passage 60 is a passage for circulating coolant water withoutpassing through radiator 40. Bypass passage 60 is constituted by pipes60 a, 60 b and thermal component 300. Pipe 60 a is provided betweenbranch portion 120 and thermal component 300. Pipe 60 b is providedbetween thermal component 300 and thermostat valve 70.

Thermal component 300 includes an EGR (Exhaust Gas Recirculation) cooler28, a pipe 29, an exhaust heat recovery unit 32, a heater core 36, athrottle body 35, and an EGR valve 34.

EGR cooler 28 cools EGR gas by means of coolant water. Throttle body 35is warmed up by coolant water to prevent occurrence of adhesion and thelike. EGR valve 34 is cooled by the coolant water. Exhaust heat recoveryunit 32 warms up the coolant water by heat of exhaust gas to therebyimprove an engine mobility during a low temperature.

Heater core 36 is used as a heater of an air-conditioning device, andperforms a heat exchange between coolant water and blast air of theair-conditioning device to heat the blast air. It should be note thatthe air-conditioning device may operate even during stopping of engine20. When a heating request is given by the air-conditioning deviceduring stopping of engine 20, electric pump 30 operates to circulatecoolant water through bypass passage 60, so that a heat exchange isperformed by heater core 36 between the coolant water and the blast airof the air-conditioning device. This lowers the temperature of thecoolant water flowing through bypass passage 60.

Thermostat valve 70 is arranged at a merging portion 110 which mergescoolant water having passed through radiator circulation passage 50 andcoolant water having passed through bypass passage 60. Merging portion110 is connected to radiator 40 through pipe 50 b and connected also topipe 60 b. The coolant water from merging portion 110 returns to asuction port of electric pump 30. Thermostat valve 70 is configured tobe switched to either a closed state or an opened state in accordancewith a temperature of coolant water flowing in thermostat valve 70 (inthe vicinity of the valve body).

In the case where a temperature of coolant water in the vicinity of thevalve body of thermostat valve 70 is less than a predeterminedvalve-opening temperature (for example, 70° C.), thermostat valve 70attains a closed state. In this case, coolant water on the side ofbypass passage 60 passes through thermostat valve 70 and is outputted towater jacket 24, but coolant water on the side of radiator circulationpassage 50 is intercepted by thermostat valve 70 and not outputted towater jacket 24. Accordingly, coolant water having taken heat fromengine 20 flows back to engine 20 (water jacket 24) without being cooledby radiator 40, so that engine 20 is warmed up.

Meanwhile, in a case where a temperature of coolant water in thevicinity of the valve body of thermostat valve 70 is equal to or higherthan the valve-opening temperature described above, thermostat valve 70is attains an opened state. In this case, coolant water from radiatorcirculation passage 50 and coolant water from bypass passage 60 passthrough thermostat valve 70 and are outputted to water jacket 24.Moreover, an opening degree of thermostat valve 70 is adjusted inaccordance with a temperature of coolant water. Accordingly, a mixtureratio between the coolant water from radiator circulation passage 50 andthe coolant water from bypass passage 60 is adjusted, so that thetemperature of the coolant water passing through water jacket 24 ismaintained at an appropriate temperature.

Engine-side coolant water temperature sensor 80 is provided at branchportion 120. Engine-side coolant water temperature sensor 80 detects atemperature of coolant water sent out from outlet 26 (hereinafter,referred to as “engine outlet water temperature ECT” or simply as “ECT”)and outputs a detection result (ECT detection value) to ECU 200. Itshould be noted that engine-side coolant water temperature sensor 80 isall necessary to be provided on a passage through which coolant wateralways circulates, and it may be provided for example on coolant waterpassage 25.

Radiator-side coolant water temperature sensor 90 is provided on pipe 50a. Radiator-side coolant water temperature sensor 90 detects atemperature of coolant water flowing into pipe 50 a of radiatorcirculation passage 50 (hereinafter, referred to as “radiator inletwater temperature RCT” or simply as “RCT”) and outputs a detectionresult (RCT detection value) to ECU 200. It should be noted thatradiator-side coolant water temperature sensor 90 is all necessary to beprovided on radiator circulation passage 50, and it may be provided forexample on pipe 50 b.

In vehicle 100 having such a configuration as described above, whenthermostat valve 70 is failed, abnormalities may occur including a closefailure in which the valve body does not open even if a coolant watertemperature in the vicinity of the valve body rises beyond thevalve-opening temperature, and an open failure in which the valve bodydoes not close even if a coolant water temperature in the vicinity ofthe valve body is lowered to be less than the valve-opening temperature.In the state where such a failure occurs, coolant water at anappropriate water temperature cannot be supplied to coolant waterpassage 25 of engine 20, so that an operation efficiency of engine 20 islowered. Therefore, it is preferable to continuously perform a failurediagnosis on whether or not thermostat valve 70 functions normallyduring operation of engine 20 to thereby find a failure in an earlystage.

Accordingly, ECU 200 performs a failure diagnosis for thermostat valve70 based on an ECT detection value received from engine-side coolantwater temperature sensor 80 and an RCT detection value received fromradiator-side coolant water temperature sensor 90. This ECU 200 isconfigured by a CPU (Central Processing Unit), a storage device, aninput/output buffer, and the like (none of these are illustrated).

As one example, ECU 200 implements a failure diagnosis with a highdiagnosis accuracy as will be described in the following. In otherwords, in a water temperature region where thermostat valve 70essentially does not open (in a water temperature region lower than thevalve-opening temperature), thermostat valve 70 is in the closed state.Therefore, theoretically, the coolant water flows into bypass passage60, and the coolant water does not flow into radiator circulationpassage 50. Therefore, a difference equal to or greater than apredetermined value occurs between the ECT detection value and the RCTdetection value. Thus, in the water temperature region where thermostatvalve 70 essentially does not open, when the difference between the ECTdetection value and the RCT detection value is less than thepredetermined value, it is determined that thermostat valve 70 isopened, in other words, an open failure occurs in thermostat valve 70.

However, indeed, even when thermostat valve 70 is normally closed, arise in the water pressure in radiator circulation passage 50 by drivingof electric pump 30 causes the coolant water in radiator circulationpassage 50 to leak out from thermostat valve 70 to coolant water passage25. In this case, even though thermostat valve 70 is in the closedstate, coolant water of the amount corresponding to the leakage flowrate of thermostat valve 70 flows from coolant water passage 25 intoradiator circulation passage 50 and is mixed with the coolant waterpresent in radiator circulation passage 50, so that radiator inlet watertemperature RCT comes close to engine outlet water temperature ECT.Since it causes the temperature difference between the ECT detectionvalue and the RCT detection value to be small, it may lower an accuracyof the failure diagnosis.

Therefore, ECU 200 performs a failure diagnosis for thermostat valve 70taking into consideration that the coolant water leaks out fromthermostat valve 70 even when thermostat valve 70 is in a normal state.Specifically, ECU 200 performs a process of calculating an estimationvalue of radiator inlet water temperature RCT based on the ECT detectionvalue and the leakage flow rate of thermostat valve 70, and diagnosingwhether or not thermostat valve 70 is failed based on a result ofcomparing the calculated RCT estimation value and the RCT detectionvalue (hereinafter, referred to as “thermostat valve failure diagnosisprocess”). This thermostat valve failure diagnosis process will bedescribed later in detail with reference to a flowchart.

Meanwhile, as described above, the heat of the coolant water heated bythe exhaust heat of engine 20 can be utilized for heating and the likeby the air-conditioning device. In this embodiment, the heat is used forheating by the air-conditioning device with use of heater core 36provided on bypass passage 60. Here, the heat of the heated coolantwater can be used even during stopping of engine 20, and the coolantwater may be circulated by operating electric pump 30 in accordance witha heating request or the like during stopping of engine 20. In thiscase, since engine 20 is stopped, thermostat valve 70 is closed, and thecoolant water does not flow into radiator circulation passage 50 butcirculate through coolant water passage 25 of engine 20 and bypasspassage 60. In that case, the coolant water circulating through coolantwater passage 25 and bypass passage 60 is deprived of heat by heatercore 36, and on the other hand the coolant water remaining in radiatorcirculation passage 50 radiates heat only in a natural manner.Therefore, it is likely to cause a situation in which the temperature ofthe coolant water circulating though coolant water passage 25 and bypasspassage 60 becomes lower than the temperature of the coolant water inradiator circulation passage 50. Accordingly, although engine outletwater temperature ECT is generally higher than radiator inlet watertemperature RCT, the relationship between engine outlet watertemperature ECT and radiator inlet water temperature RCT is inversed, sothat erroneous determination may be made in the failure diagnosis.

FIG. 2 represents one example of a change in the engine coolant watertemperature before and after starting of engine 20. Referring to FIG. 2,it is assumed that, before time t1, engine 20 is stopped, and use of aheater and the like during stopping of the engine causes a situation ofECT detection value <RCT detection value. It should be noted that thefailure diagnosis for thermostat valve 70 is not performed duringstopping of engine 20.

It is assumed that engine 20 is started at time t1. In that case, theengine coolant water is heated by the exhaust heat of engine 20, and theECT detection value indicating the temperature of the coolant water atthe engine outlet starts to rise. It should be noted that, immediatelyafter starting of engine 20, the temperature of the coolant water islower than the valve-opening temperature of thermostat valve 70, andthermostat valve 70 is closed, so that no rise in the RCT detectionvalue can be seen. Then, until time t2, the ECT detection value <RCTdetection value continues, and it attains the ECT detection value >RCTdetection value on or after time t2.

As can be seen, even when engine 20 is started at time t1, the ECTdetection value <RCT detection value continues until time t2. Therefore,if the failure diagnosis is started before time t2, erroneousdetermination is made since the relationship of ECT detection value >RCTdetection value which should be essentially provided is inversed.Therefore, in this embodiment, taking into consideration the erroneousdetermination region between times t1 and t2, in the case where electricpump operates in accordance with a heating request or the like of theair-conditioning device during stopping of engine 20 (thermostat valve70 is in the closed state), ECU 200 delays starting of the failurediagnosis process for thermostat valve 70 performed after starting ofengine 20 as compared to the case where electric pump 30 does notoperate during stopping of engine 20. Accordingly, the failure diagnosisis avoided in the state where the relationship between the ECT detectionvalue and the RCT detection value is inversed, so that the erroneousdetermination in the failure diagnosis is suppressed.

FIG. 3 is a flowchart for describing procedures of the thermostat valvefailure diagnosis process executed by ECU 200 shown in FIG. 1. Theprocess shown in this flowchart is executed at the time of startingengine 20, for example, at the time of starting engine after idlingstop. In the case where vehicle 100 is a hybrid vehicle, the process isexecuted further at the time of starting an engine when switched from EVtraveling with use of a drive force of a motor after stopping engine 20to HV traveling with operation of engine 20. This flowchart is achievedby executing a program stored in ECU 200 at predetermined cycles, andthe process of some steps can be achieved by constructing a dedicatedhardware (electronic circuit).

Referring to FIG. 3, ECU 200 calculates an estimation value of radiatorinlet water temperature RCT (RCT estimation value) based on the ECTdetection value received from engine-side coolant water temperaturesensor 80, and a leakage flow rate into radiator circulation passage 50when thermostat valve 70 is in the closed state (Step S10).Specifically, ECU 200 can calculate the RCT estimation value with use ofthe following expression as one example.

RCT estimation value=(ECT detection value×leakage flow rate+RCTestimation value (previous value)×(pipe volume−leakage flow rate))/pipevolume  (1)

In Expression (1), the RCT estimation value is calculated based on theassumption that the coolant water with the ECT detection value and thecoolant water with the RCT estimation value (previous value) are evenlymixed in accordance with a ratio of the leakage flow rate with respectto the pipe volume.

Herein, the leakage flow rate may be a fixed value determined in advancebased on an experimental result or the like, or it may be a variablevalue set to have a larger value as the flow rate of electric pump 30for example is larger. The pipe volume is a volume of the pipe throughwhich the coolant water flows from engine-side coolant water temperaturesensor 80 to radiator-side coolant water temperature sensor 90. Itshould be noted that the calculation accuracy can be improved bydividing the pipe into any number of regions and applying the expressionof (1) described above to each divided region.

Next, ECU 200 executes the process of determining whether or not aprecondition for executing an open failure diagnosis process forthermostat valve 70 (hereinafter, simply referred to as “diagnosisprecondition”) is met (Step S20). The contents of this process will bedescribed in detail in FIG. 4 which will be described later.

Then, ECU 200 determines whether or not the thermostat open failurediagnosis process will be performed based on the process result of StepS20 (Step S30). When it is determined that the diagnosis precondition isnot met (NO in Step S30), ECU 200 terminates the process withoutexecuting the thermostat open failure diagnosis process (processes ofSteps S40 to S60). In other words, ECU 200 prohibits the thermostat openfailure diagnosis process in the case where the diagnosis preconditionis not met.

On the other hand, when it is determined in Step S30 that the diagnosisprecondition is met (YES in Step S30), ECU 200 executes the thermostatopen failure diagnosis process (the processes of Steps S40 to S60).

In other words, ECU 200 determines whether or not the RCT detectionvalue received from radiator-side coolant water temperature sensor 90 ishigher than the RCT estimation value calculated in Step S10 (Step S40).Then, when the RCT detection value is higher than the RCT estimationvalue (YES in Step S40), ECU 200 determines that thermostat valve 70 isin the open failure state (Step S50). This is because when thermostatvalve 70 is in the open failure state, the heated coolant water of theamount larger than the expected leakage flow rate flows into radiatorcirculation passage 50, and a situation in which the RCT detection valueis higher than the RCT estimated value occurs. On the other hand, whenthe RCT detection value is equal to or lower than the RCT estimationvalue (NO in Step S40), ECU 200 determines that thermostat valve 70 isnormal (Step S60).

FIG. 4 is a flowchart representing the process procedures for thediagnosis precondition determination executed in Step S20 of FIG. 3.Referring to FIG. 4, ECU 200 determines whether or not the monitoringprecondition is met. The monitoring precondition is a condition set as aprecondition for monitoring a water temperature rise quantity ΔECTindicating a rise in the coolant water temperature from starting of theengine in Steps S130 and S160 which will be described later. As oneexample, ECU 200 determines that the monitoring precondition is met whenall of the following conditions (a) to (f) are met.

(a) After current starting of an engine, the thermostat failurediagnosis is not completed.

(b) The ECT detection value is less than the valve-opening temperature(for example, 70° C.) of thermostat valve 70.

(c) The ECT detection value at the time of starting the engine isincluded in the range of −10° C. to +56° C.

(d) The engine is started.

(e) The time change quantity of the ECT detection value is equal to orgreater than a predetermined value (for example, 0.1° C./second).

(f) Engine-side coolant water temperature sensor 80 and radiator-sidecoolant water temperature sensor 90 are normal.

Condition (a) provides the premise that the thermostat failure diagnosisis performed once between starting of engine 20 and stopping next.Condition (b) is a condition for assuring that thermostat valve 70 isessentially (if it is normal) closed. Conditions (c) and (d) areconditions for assuring that the ECT detection value increases in amanner capable of performing the thermostat failure diagnosis afterstarting the engine. Condition (e) is a condition for assuring a rise inthe engine water temperature after starting the engine. Condition (f) isa condition for assuring a reliability of the ECT detection value or theRCT detection value. It should be noted that, as the monitoringprecondition, conditions (a) to (f) described above may be selected asneeded.

When it is determined in Step S110 that the monitoring precondition isnot met (NO in Step S110), ECU 200 shifts the process to Step S180 anddetermines that the diagnosis precondition is not met (Step S180).

When it is determined in Step S110 that the monitoring precondition ismet (YES in Step S110), ECU 200 determines whether or not electric pump30 operates during previous stopping of the engine (from previousstopping of the engine to the current starting of the engine) (StepS120).

In the case where electric pump 30 operates during stopping of theengine (YES in Step S120), ECU 200 determines whether or not the watertemperature rise quantity ΔECT indicating a rise in the quantity of theECT detection value after starting of engine 20 is larger than apredetermined value A (>predetermined value B) (Step S130). Thispredetermined value A is a determination value of the diagnosisprecondition for the case where electric pump 30 operates duringstopping of the engine, and it is larger than a determination value B(default value) of the diagnosis precondition for the case whereelectric pump 30 does not operate during stopping of the engine. As oneexample, predetermined value B is 1° C., and predetermined value A is 3°C. Accordingly, starting of the failure diagnosis for the case whereelectric pump 30 operates during stopping of the engine can be delayedas compared to the case where electric pump 30 does not operate duringstopping of the engine.

Then, when it is determined in Step S130 that water temperature risequantity ΔECT is larger than predetermined value A (YES in Step S130),ECU 200 determines that the diagnosis precondition is met (Step S140).When it is determined in Step S130 that water temperature rise quantityΔECT is less than or equal to predetermined value A (NO in Step S130),it is determined that the diagnosis precondition is not met (Step S150).

On the other hand, when it is determined in Step S120 that electric pump30 does not operate during previous stopping of the engine (NO in StepS120), ECU 200 determines whether or not water temperature rise quantityΔECT is larger than predetermined value B (Step S160). When it isdetermined in Step S160 that water temperature rise quantity ΔECT islarger than predetermined value B (YES in Step 160), ECU 200 determinesthat the diagnosis precondition is met (Step S170). When it isdetermined in Step S160 that water temperature rise quantity ΔECT isless than or equal to predetermined value B (NO in Step S160), ECU 200determines that the diagnosis precondition is not met (Step S180).

As described above, in this engine cooling device 10, in the case whereelectric pump 30 operates in accordance with a heating request or thelike of the air-conditioning device during stopping of engine 20,starting of the failure diagnosis performed after starting of engine 20is delayed as compared to the case where electric pump 30 does notoperate during stopping of engine 20, so that starting of the failurediagnosis of thermostat valve 70 in the state where the relationshipbetween engine outlet water temperature ECT and radiator inlet watertemperature RCT is inversed can be avoided. Thus, according to thisengine cooling device 10, erroneous determination can be suppressed inthe failure diagnosis of thermostat valve 70.

Moreover, while the failure diagnosis for thermostat valve 70 isperformed based on the temperature of the coolant water, according tothis engine cooling device 10, starting of the failure diagnosis isadjusted based on the coolant water temperature, so that the starttiming of the failure diagnosis can be adjusted with a high accuracy.

Moreover, according to this engine cooling device 10, the failurediagnosis of thermostat valve 70 is performed taking into considerationthe leakage flow rate through radiator circulation passage 50 in theclosed state of thermostat valve 70, so that the failure diagnosis canbe performed with a high accuracy.

Modified Example 1

In the embodiment described above, starting of the thermostat valvefailure diagnosis process after starting of the engine (the diagnosisprecondition is met) is delayed based on the rise quantity (ΔECT) of theengine coolant water temperature (ECT detection value) after starting ofengine 20. In place of water temperature rise quantity ΔECT, anintegrated amount of the intake air volume into engine 20 from startingof engine 20 may be used. This is because the integrated intake airvolume from starting of engine 20 may represent a tendency of the risein temperatures of engine 20 and the coolant water.

The overall configuration of the vehicle in this Modified Example 1 isthe same as vehicle 100 shown in FIG. 1. Moreover, the procedures of theoverall process of the thermostat valve failure diagnosis executed byECU 200 of this Modified Example 1 is the same as the process proceduresshown in FIG. 3.

FIG. 5 is a flowchart representing process procedures of the diagnosisprecondition determination (the process executed in Step S20 of FIG. 3)in this Modified Example 1. Referring to FIG. 5, this flowchartincludes, in the flowchart shown in FIG. 4, Steps S132 and S136 in placeof Steps S130 and S160.

In other words, when it is determined in Step S120 that electric pump 30operates during previous stopping (YES in Step S120), ECU 200 determineswhether or not an integrated intake air volume indicating an integratedamount of the intake air volume into engine 20 from starting of engine20 is greater than a predetermined value C (>predetermined value D)(Step S132). It should be noted that predetermined value C is adetermination value of the diagnosis precondition for the case whereelectric pump 30 operates during stopping of the engine, and it islarger than determination value D (default value) for the case whereelectric pump 30 does not operate during stopping of the engine. As oneexample, predetermined value C is 50 g, and predetermined value D is 20g. It should be noted that the intake air volume into engine 20 can bedetected with use of an air flow meter. With predetermined valueC >predetermined value D, starting of the failure diagnosis for the casewhere electric pump 30 operates during stopping of the engine can bedelayed as compared to the case where electric pump 30 does not operateduring stopping of the engine.

Then, when it is determined in Step S132 that the integrated intake airvolume is larger than predetermined value C (YES in Step S132), theprocess is shifted to Step S140, and it is determined that the diagnosisprecondition is met. When it is determined that the integrated intakeair volume is equal to or less than predetermined value C in Step S132(NO in Step S132), the process is shifted to Step S150, and it isdetermined that the diagnosis precondition is not met.

On the other hand, when it is determined in Step S120 that electric pump30 does not operate during previous stopping of the engine (NO in StepS120), ECU 200 determines whether or not the integrated intake airvolume is larger than predetermined value D (Step S162). Then, when itis determined that the integrated intake air volume is larger thanpredetermined value D (YES in Step S162), the process is shifted to StepS170, and it is determined that the diagnosis precondition is met. Whenit is determined in Step S162 that the integrated intake air volume isless than or equal to predetermined value D (NO in Step S162), theprocess is shifted to Step S180, and it is determined that the diagnosisprecondition is not met.

Also by this Modified Example 1, in the case where electric pump 30operates in accordance with a heating request or the like of theair-conditioning device during stopping of engine 20, starting of thefailure diagnosis performed after starting of engine 20 can be delayedas compared to the case where electric pump 30 does not operate duringstopping of engine 20. Accordingly, similarly to the embodimentdescribed above, erroneous determination can be suppressed in thefailure diagnosis of thermostat valve 70.

Modified Example 2

While starting of the thermostat valve failure diagnosis from startingof engine 20 (the diagnosis precondition is met) is delayed based on theintegrated intake air volume from starting of engine 20 in ModifiedExample 1 described above, time from starting of engine 20 can bemeasured to use an elapsed time after starting of the engine.Accordingly, the process of capturing a detection signal of a sensor andthe calculation process are not required, so that the process of ECU 200is simplified. Moreover, starting of the failure diagnosis can beadjusted without being affected by an abnormality of the sensor and ameasurement accuracy.

The overall configuration of the vehicle in this Modified Example 2 isthe same as that of vehicle 100 shown in FIG. 1. Moreover, theprocedures of the overall process of the thermostat valve failurediagnosis executed by ECU 200 in this Modified Example 2 are the same asthe process procedures shown in FIG. 3.

FIG. 6 is a flowchart representing the process procedures fordetermining the diagnosis precondition (the process executed in Step S20of FIG. 3) in this Modified Example 2. Referring to FIG. 6, thisflowchart includes, in the flowchart shown in FIG. 4, Steps S134 andS164 in place of Steps S130 and S160.

In other words, when it is determined in Step S120 that electric pump 30operates during previous stopping of the engine (YES in Step S120), ECU200 determines whether or not an elapsed time from starting of engine 20exceeds a predetermined value T1 (>predetermined value T2) (Step S134).It should be noted that predetermined value T1 is a determination valueof the diagnosis precondition for the case where electric pump 30operates during stopping of the engine, and it is larger thandetermination value T2 (default value) of the diagnosis precondition forthe case where electric pump 30 does not operate during stopping of theengine. As one example, predetermined value T1 is 5 seconds, andpredetermined value T2 is 2 seconds. It should be noted that the elapsedtime from starting of engine 20 can be measured by means of a timer orthe like not illustrated in the drawings. With predetermined valueT1>predetermined value T2, starting of the failure diagnosis for thecase where electric pump 30 operates during stopping of the engine canbe delayed as compared to the case where electric pump 30 does notoperate during stopping of the engine.

Then, when it is determined in Step S134 that the elapsed time exceedspredetermined value T1 (YES in Step S134), the process is shifted toStep S140, and it is determined that the diagnosis precondition is met.When it is determined in Step S134 that the elapsed time is less than orequal to predetermined value T1 (NO in Step S134), the process isshifted to Step S150, and it is determined that the diagnosisprecondition is not met.

On the other hand, when it is determined in Step S120 that electric pump30 does not operate during previous stopping of the engine (NO in StepS120), ECU 200 determines whether or not the elapsed time exceedspredetermined value T2 (Step S164). Then, when it is determined that theelapsed time exceeds predetermined value T2 (YES in Step S164), theprocess is shifted to Step S170, and it is determined that the diagnosisprecondition is met. When it is determined in Step S164 that the elapsedtime is less than or equal to predetermined value T2 (NO in Step S164),the process is shifted to Step S180, and it is determined that thediagnosis precondition is not met.

Also by this Modified Example 2, in the case where electric pump 30operates in accordance with a heating request or the like of theair-conditioning device during stopping of engine 20, starting of thefailure diagnosis performed after starting of engine 20 can be delayedas compared to the case where electric pump 30 does not operate duringstopping of engine 20. Accordingly, similarly to the embodimentdescribed above, erroneous determination can be suppressed in thefailure diagnosis of thermostat valve 70.

Moreover, in this Modified Example 2, starting of the failure diagnosisis adjusted based on the elapsed time from starting of engine 20.Therefore, the process of capturing a detection signal of a sensor andthe calculation process are not required. Thus, according to thisModified Example 2, the process of ECU 200 can be simplified. Moreover,starting of the failure diagnosis can be adjusted without being affectedby an abnormality of the sensor and the measurement accuracy.

It should be noted that, while the failure diagnosis of thermostat valve70 is performed taking into consideration the leakage flow rate throughradiator circulation passage 50 in the closed state of thermostat valve70 in the embodiment described above and Modified Examples 1 and 2thereof, the method of the failure diagnosis is not limited to suchmethods. For example, the present invention is applicable for the casewhere the failure diagnosis is performed based on the comparison betweenECT detection value and the RCT detection value in more simple manner.

It should be noted that this invention is applicable also to a hybridvehicle provided with a traveling motor in addition to engine 20 and avehicle not provided with the traveling motor. In the vehicle notprovided with the traveling motor, this invention is applicable tostarting of the engine after idling stop or after IG-on operation by auser. In the hybrid vehicle, this invention is further applicable tostarting of engine when switching from the EV traveling to the HVtraveling.

It should be noted that, in the description above, engine 20 correspondsto one example of the “internal combustion engine” of this invention,and heater core 36 corresponds to one example of the “heat exchanger” ofthis invention. Moreover, engine-side coolant water temperature sensor80 corresponds to one example of the “first temperature sensor” of thisinvention, and radiator-side coolant water temperature sensor 90corresponds to one example of the “second temperature sensor” of thisinvention.

Although the present invention has been described and illustrated indetail, it should be understood that the same is by way of illustrationand example only and is not to be taken by way of limitation. The scopeof the present invention is indicated by the scope of claims, andincludes meaning equivalent to that of the scope of claims and all themodification within the scope.

What is claimed is:
 1. A cooling device for an internal combustionengine, comprising: a coolant water passage formed in said internalcombustion engine; a radiator configured to cool coolant water; aradiator circulation passage configured to allow coolant waterdischarged from said coolant water passage to pass through said radiatorand return to said coolant water passage; a bypass passage configured toallow coolant water discharged from said coolant water passage to returnto said coolant water passage without passing through said radiator; aheat exchanger provided on said bypass passage and utilizing heat ofsaid coolant water; and a thermostat valve connected to said radiatorcirculation passage and said bypass passage, said thermostat valve beingswitched, in accordance with a temperature of coolant water flowing insaid thermostat valve, to either a closed state of intercepting coolantwater from said radiator circulation passage and outputting coolantwater from said bypass passage to said coolant water passage, or anopened state of outputting coolant water from said radiator circulationpassage and coolant water from said bypass passage to said coolant waterpassage, said cooling device further comprising: an electric pumpconfigured to allow coolant water to circulate; a first temperaturesensor configured to detect a temperature of coolant water in saidcoolant water passage; a second temperature sensor configured to detecta temperature of coolant water in said radiator circulation passage; anda control device configured to perform a failure diagnosis for saidthermostat valve after starting of said internal combustion engine basedon an output of said first temperature sensor and an output of saidsecond temperature sensor, wherein when said electric pump operates inaccordance with an operation request of said heat exchanger duringstopping of said internal combustion engine, said thermostat valveattains the closed state, and in a case where said electric pumpoperates during stopping of said internal combustion engine, saidcontrol device delays starting of said failure diagnosis performed afterstarting of said internal combustion engine as compared to a case wheresaid electric pump does not operate during stopping of said internalcombustion engine.
 2. The cooling device for an internal combustionengine according to claim 1, wherein said control device starts saidfailure diagnosis when a rise quantity of a coolant water temperature,which is detected by said first temperature sensor, from starting ofsaid internal combustion engine exceeds a predetermined value, and afirst value indicating said predetermined value for the case where saidelectric pump operates during stopping of said internal combustionengine is larger than a second value indicating said predetermined valuefor the case where said electric pump does not operate during stoppingof said internal combustion engine.
 3. The cooling device for aninternal combustion engine according to claim 2, wherein said controldevice calculates an estimation value of the coolant water temperaturein said radiator circulation passage based on a leakage flow ratethrough said radiator circulation passage in the closed state of saidthermostat valve and on an output of said first temperature sensor, anddiagnoses that said thermostat valve is failed in a case where an outputvalue of said second temperature sensor is larger than the calculatedestimation value.
 4. The cooling device for an internal combustionengine according to claim 1, wherein said control device integrates anintake air volume to said internal combustion engine from starting ofsaid internal combustion engine, and starts said failure diagnosis whenthe integrated value of said intake air volume exceeds a predeterminedvalue, and a first value indicating said predetermined value for thecase where said electric pump operates during stopping of said internalcombustion engine is larger than a second value indicating saidpredetermined value for the case where said electric pump does notoperate during stopping of said internal combustion engine.
 5. Thecooling device for an internal combustion engine according to claim 4,wherein said control device calculates an estimation value of thecoolant water temperature in said radiator circulation passage based ona leakage flow rate through said radiator circulation passage in theclosed state of said thermostat valve and on an output of said firsttemperature sensor, and diagnoses that said thermostat valve is failedin a case where an output value of said second temperature sensor islarger than the calculated estimation value.
 6. The cooling device foran internal combustion engine according to claim 1, wherein said controldevice starts said failure diagnosis when an elapsed time from startingof said internal combustion engine exceeds a predetermined value, and afirst value indicating said predetermined value for the case where saidelectric pump operates during stopping of said internal combustionengine is larger than a second value indicating said predetermined valuefor the case where said electric pump does not operate during stoppingof said internal combustion engine.
 7. The cooling device for aninternal combustion engine according to claim 6, wherein said controldevice calculates an estimation value of the coolant water temperaturein said radiator circulation passage based on a leakage flow ratethrough said radiator circulation passage in the closed state of saidthermostat valve and on an output of said first temperature sensor, anddiagnoses that said thermostat valve is failed in a case where an outputvalue of said second temperature sensor is larger than the calculatedestimation value.